Thomas P. Ketterl

A Wireless Robot for Networked Laparoscopy

State-of-the-art laparoscopes for minimally invasive abdominal surgery are encumbered by cabling for power, video, and light sources. Although these laparoscopes provide good image quality, they interfere with surgical instruments, occupy a trocar port, require an assistant in the operating room to control the scope, have a very limited field of view, and are expensive. MARVEL is a wireless Miniature Anchored Robotic Videoscope for Expedited Laparoscopy that addresses these limitations by providing an inexpensive in vivo wireless camera module (CM) that eliminates the surgical-tool bottleneck experienced by surgeons in current laparoscopic endoscopic single-site (LESS) procedures. The MARVEL system includes1) multiple CMs that feature awirelessly controlled pan/tilt camera platform, which enable a full hemisphere field of view inside the abdominal cavity, wirelessly adjustable focus, and a multiwavelength illumination control system; 2) a master control module that provides a near-zero latency video wireless communications link, independent wireless control for multiple MARVEL CMs, digital zoom; and 3) a wireless human-machine interface that gives the surgeon full control over CM functionality. The research reported in this paper is the first step in developing a suite of semiautonomous wirelessly controlled and networked robotic cyberphysical devices to enable a paradigm shift in minimally invasive surgery and other domains such as wireless body area networks.

A 2.45 GHz Phased Array Antenna Unit Cell Fabricated Using 3-D Multi-Layer Direct Digital Manufacturing

This paper reports on the design, fabrication and characterization of a 3-D printed RF front end for a 2.45 GHz phased array unit cell. The printed unit cell, which includes a circularly-polarized dipole antenna, a miniaturized capacitive-loaded open-loop resonator filter and a 4-bit phase shifter, is fabricated using a direct digital manufacturing (DDM) approach that integrates fused deposition of thermoplastic substrates with micro-dispensing for deposition of conductive traces. The individual components are combined in a passive phased array antenna unit cell comprised of seven stacked substrate layers with seven conductor layers. The measured return loss of the unit cell is > 12 dB across the 2.45 GHz ISM band and the measured gain is -11 dBi including all components. Experimental and simulation-based characterization is performed to investigate electrical properties of as-printed materials, in particular the inhomogeneity of printed thick-film conductors and substrate surface roughness. The results demonstrate the strong potential for fully-printed RF front ends for light weight, low cost, conformal and readily customized applications.

MARVEL: A wireless Miniature Anchored Robotic Videoscope for Expedited Laparoscopy

This paper describes the design and implementation of a Miniature Anchored Robotic Videoscope for Expedited Laparoscopy (MARVEL) and Camera Module (CM) that features wireless communications and control. The CM decreases the surgical-tool bottleneck experienced by surgeons in state-of-the art Laparoscopic Endoscopic Single-Site (LESS) procedures for minimally invasive abdominal surgery. The system includes: (1) a near-zero latency video wireless communications link, (2) a pan/tilt camera platform, actuated by two motors that provides surgeons a full hemisphere field of view inside the abdominal cavity, (3) a small wireless camera, (4) a wireless illumination control system, and (5) a wireless human-machine interface (HMI) to control the CM. An in-vivo experiment on a porcine subject was carried out to test the performance of the system. The robotic design is a Research Platform for a broad range of experiments in a range of domains for faculty and students in the Colleges of Engineering and Medicine and at Tampa General Hospital. This research is the first step in developing semi-autonomous wirelessly controlled and networked laparoscopic devices to enable a paradigm shift in minimally invasive surgery and other domains such as Wireless Body Area Networks.

In vivo wireless communication channels

In this paper we perform signal strength and channel impulse response simulations using an accurate human body model and we investigate the variation in signal loss at different RF frequencies as a function of position around the human body. It was observed that significant variations in received signal strength (RSS) occurred with changing position of the external receive antenna at a fixed distance from the internal antenna. The variations were even more profound at the highest frequency, where just a 5° of movement causes an increase of RSS up to 20 dB. Wideband scattering parameters were also obtained and the channel impulse response was calculated. A greater amount of dispersion through the abdomen has been observed than was expected based on human body geometry.

A micromachined tunable CPW resonator

This paper presents a novel tunable microwave resonator, consisting of a CPW spiral inductor with a cantilever interconnect structure. Tuning was achieved by applying a DC bias between the input and output of the resonator circuit. An observable resonance tuning between 3 and 7 GHz was accomplished by applying a bias from 0 to 40 V. Corresponding Q-factors between 17 and 20 were obtained in this tuning range.

3D multi-layer additive manufacturing of a 2.45 GHz RF front end

Digital additive manufacturing (AM) is emerging as a promising technology for next-generation RF systems. AM processes that combine multiple materials in a single build and can produce volumetric designs are especially interesting for 3D structural electronics. This paper reports on 3D AM fabricated components for a 2.45 GHz RF front end, specifically a circularly-polarized dipole antenna, a miniaturized capacitive-loaded open-loop resonator filter and a switched-line phase shifter. The printing process integrates fused deposition of thermoplastic substrates with micro-dispensing for deposition of conductive traces. These initial results demonstrate the strong potential for fully-printed RF front ends for light weight, low cost, conformal and readily customized applications.

SAR and BER evaluation using a simulation test bench for in vivo communication at 2.4 GHz

We present a simulation method and results that utilizes accurate electromagnetic field simulations to study the maximum allowable transmitted power levels from in vivo devices to achieve a required bit error rates (BER) at the external node (receiver) while maintaining the specific absorption rate (SAR) under a required threshold. The BER of the communication can be calculated using the derived power threshold for a given modulation scheme. These results can be used to optimize the transmitted power levels while assuring that the safety guidelines in terms of the resulting SAR of transmitters placed in any location inside the human body are met. To evaluate the SAR and BER, a software-based test bench that allows an easy way to implement field solver solutions directly into system simulations was developed. To demonstrate the software-based test bench design, a complete OFDM-based communication (IEEE 802.11g) for the in vivo environment was simulated. Results showed that for cases when noise levels increase or the BER becomes more stringent, a relay network or the use of multiple receive antennas, such as in a MIMO system, will be become necessary to achieve high data rate communication.

Multimaterial and Multilayer Direct Digital Manufacturing of 3-D Structural Microwave Electronics

Direct digital manufacturing (DDM) is an emerging technology that is finding its place across a wide array of industries and applications as a cost-effective solution for low volume and mass customizable production. This technology encompasses a class of digital manufacturing techniques which can be combined to enable multimaterial fabrication and postprocessing. One of the promising applications for DDM is structural electronics, where lightweight printed plastics provide mechanical support as a fixture, package, or structural member and also host the electrical interconnects and devices, all in a contiguous fashion. Microwave structural electronics is a specific class of such systems for which the printing resolution as well as electrical and surface properties of the materials are especially important. This paper presents the current state of DDM technology, fundamental research into the electrical and mechanical properties of as-printed structures, and novel 3-D printed structures operating from C-band through Ku-band.

MIMO in vivo

We present the performance of MIMO for in vivo environments, using ANSYS HFSS and their complete human body model, to determine the maximum data rates that can be achieved using an IEEE 802.11n system. Due to the lossy nature of the in vivo medium, achieving high data rates with reliable performance will be a challenge, especially since the in vivo antenna performance is strongly affected by near-field coupling to the lossy medium and the signals levels will be limited by specified specific absorption rate (SAR) levels. We analyzed the bit error rate (BER) of a MIMO system with one pair of antennas placed in vivo and the second pair placed inside and outside the body at various distances from the in vivo antennas. The results were compared to SISO arrangements and showed that by using MIMO in vivo, significant performance gain can be achieved, and at least two times the data rate can be supported with SAR limited transmit power levels, making it possible to achieve target data rates in the 100 Mbps.

Modeling the wireless in vivo path loss

Our long-term research goal is to model the in vivo wireless channel. As a first step towards this goal, in this paper we performed in vivo path loss measurements at 2.4GHz and make a comparison with free space path loss. We calculate the path loss by using the electric field radiated by a Hertzian-Dipole located inside the abdominal cavity. The simulations quantify and confirm that the path loss falls more rapidly inside the body than outside the body. We also observe fluctuations of the path loss caused by the inhomogeneity of the human body. In comparison with the path loss measured with monopole antennas, we conclude that the significant variations in Received Signal Strength is caused by both the angular dependent path loss and the significantly modified in vivo antenna effects. Index Terms — In vivo propagation, ex vivo communication, path loss model, Hertzian-Dipole, angular dependentOur long-term research goal is to model the in vivo wireless channel. As a first step towards this goal, in this paper we performed in vivo path loss measurements at 2.4 GHz and make a comparison with free space path loss. We calculate the path loss by using the electric field radiated by a Hertzian-Dipole located inside the abdominal cavity. The simulations quantify and confirm that the path loss falls more rapidly inside the body than outside the body. We also observe fluctuations of the path loss caused by the inhomogeneity of the human body. In comparison with the path loss measured with monopole antennas, we conclude that the significant variations in Received Signal Strength is caused by both the angular dependent path loss and the significantly modified in vivo antenna effects.